1. Field of the Invention
The technology relates to the snack food industry, and more particularly to an apparatus for the popping of pellets under heat and pressure to form snack foods.
2. Description of the Related Art
The production of snacks cakes of popped grains, such as for example rice cakes, is a process that includes subjecting the grains to heat and pressure in popping machines that are either hydraulically or pneumatically driven. During the popping process, the rice grains are subjected to both heat and pressure and become highly expanded. The resultant cakes have a low density compared to the rice grains due to volume expansion that takes place, and have significant thickness, for example, commonly in the range of about 1 inch (2.5 cm) or more, for an about 2-3 inch (5.0 to 7.5 cm) diameter cake.
Popping machines are also used in the production of a chip-like snack, from pellets of dough. These production processes may include a single compression step during which there is melting, heating, and expansion of the pellets into the final snack food product. In other cases, a double compression popping process may be used wherein a second compression follows the expansion of the product at the end of the first compression step to produce a chip-like snack food product, exemplified by Lay's® Air Pops (Lay's is a registered trademark of Frito Lay, USA). Typically, the second compression follows very rapidly after the first, for example, within about 5 to 10 milliseconds. Thus, compressive force for the second compression must build up very rapidly, after relaxation of compression at the end of the first compression step. For this reason, processes that include a second compression have been carried out on hydraulic-driven popping machines. Hydraulic-driven popping machines have a closed loop of hydraulic drive fluid, and are able to react very rapidly in terms of raising hydraulic fluid pressure to apply compressive force, releasing pressure and then, within a period measured in the millisecond range, again becoming pressurized to provide a second compressive force. In other words, hydraulic-driven machines can cycle at high speed from compression to relaxation, and back to compression.
Pneumatic machines are used in “single” compression popping processes. These machines lack the high speed pressure cycling capability of the hydraulic-driven machines, for several reasons. These reasons include, for example, that pneumatic-driven machines do not have a closed pneumatic circuit. Instead, they relieve pressure to the atmosphere after the first compression step. If there is to be a second compression step, atmospheric intake air must then be compressed for the second compression step. The rate at which a compressor can provide compressed air, starting from atmospheric pressure at air intake, imposes a time limitation on the development of sufficient compressive force. The time to develop sufficient compressive force may be in the multi-second range, for example of the order of about 8 seconds, depending upon the compressor and ancillaries, and is not in the millisecond range. As a result, in the prior art the double compression popping process to produce chip-like snack foods, which requires applying a second compression step within milliseconds of the first, is carried out on a hydraulic-driven popping machine.